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G. E. MUELLER. TELEPHONE CALL REGISTER AND SYSTEM. APPLICATION man NOV. I9, 1906.

Patented Aug. 1, 1916.

8 SHEETSSHEET 1. L

e. E. MUELLER TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATION FILED NOV. 19. I906.

Patented Aug. 1, 1916.

8 SHEETS-SHEET 2.

G. E. MUELLER.-

TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATHJN FILED NOV- HL 1906- 1 To Patented Aug. 1, 1916.

8 SHEET$-SHEET 3- G. E MUELLER.

TELEPHONE CALL REGISTER AND SYSTEM. APPLICATION HLED NOV. I9, 1906.

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Patented Aug. 1, 1916.

8 SHEETS-SHEET 4.

. G. E. MUELLER.

TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATION FILED NOV. 19, 1906.

Patented Aug. 1, 1916.

8 SHEETS-SHEET 5 G E. MUELLER.

TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATION FILED NOV. 19. I906.

T.,T93,W9. Patented Aug. 1, 1916.

8 SHEETS-SHEET 6.

G. E. MUELLER.

TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATION FILED NOV-19,1906. V

Patented Aug. 1

8 SHEETS-SHEET 7.

G. E. MUELLER.

TELEPHONE CALL REGISTER AND SYSTEM.

APPLICATION FILED NOV. 19, 1906.

l L 93., 1 9., Patented Aug. 1, 1916.

8 SHEETS-SHEET 8- GEORGE E. MUELLER, 0F AURORA, ILLINOIS,

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

KJELJLOGG: SWITCHBOARD SUPPLY COMPANY, A CORPORATION OF ILLINOIS.

TELEPHONE-CALI: REGISTER AND SYSTEM. I

earts.

Specification of Letters Patent.

Patented drug. 1, 191 6.

Application filed November 19, 1906. Serial No. 344,114.

To all whom it may concern Be it known that I, GEORGE E. MUELLER a citizen of the United States, resident of Aurora, county of Kane, and State of l[l1i nois, have invented new and useful Improvements in Telephone-Call Registers and Systems, of which the following is a specification.

My invention relates more particularly to automatic telephone systems having a central source of current from which subscribers transmitters are energized for talking, but is in its broader aspects not to be limited to its employment in connection with such systems.

In the accompanying drawings, T have illustrated structures for registering the number of telephone calls capable of employment in connection with various telephone systems, as for instance, such a system as that illustrated in the patent to Alfred H. Dyson, telephone pay-station devices, No. 830,653, issued September 11, 1906, and also in connection with the telephone system more particularly hereinafter shown and described; the more particular object of my invention being to produce a call register system wherein the calls are automatically registered without the assistance of a central ofiice operator.

Referring to the drawings, Figure 1, consisting of Sheets 1, 2 3, illustrates the circuits of an automatic common battery telephone system arranged in accordance with my invention; Figs. 2 and 3 show front and side views of a master-switch; Fig. 4c is a top sectional view of a line selector; Figs. 5 and 6 illustrate circuit-changing mechanism of a first selector; Figs. 7 and 8 illustrate, respectively, an over-run switch and a primary off-normal switch for the line selector; Figs. 9, 10 and 11 are, respectively, left, front and right elevations of a line selector; Figs. 12, 13 and 14 are similar views of a connector; and Figs. 15, 16, 17, 18, 19 and 20 illustrate various embodiments of my invention shown in connection with automatic telephone substation circuits and apparatus.

1 shall first describe the automatic telephone system herein shown, which in itself I do not claim as my invention, and-shall thereafter point out the various features of my invention as relating thereto and to the system of the patent above mentioned.

Referring first to Fig. 1, the system there illustrated may be considered as a ten thousand line system. Assuming such to be the case, each subscribers line, such as those of substations A. and B, extends to the exchange and is there provided with its individual passive multiple line contacts 2020-2224, appearing with those of ninety-nine other lines in the contact banks of ten line selectors, such as D. Inasmuch as ten thousand lines are assumed, there will have to be in all one hundred such groups of lines, each with its ten line selectors, making a total of one thousand such selectors. Each such line selector has permanent connection with a particular first selector such as E, which is automatically brought under the control of currents to be sent over the calling line by the operation of the line selector D. The first selector, by its adjustable wipers, gives the calling subscriber access to one hundred second selectors, there being ten of these representing each one thousand lines of the exchange.v Contacts of the second selector engaged by the first selectors are, of course, multiplied in the usual manner to a large number of first selector contact banks and would ordinarily be multiplied one hundred times or to one hundred such banks.

Responsive to currents transmitted over the calling line by the subscriber, the first selector is caused to select the group of second selectors corresponding to the one thousands digit of the called number; the first selector then automatically selects the first idle second selector of the selected group, placing it under the control of the calling line.

The second selector, by its wipers, gives access to one hundred connectors divided in tens groups of ten switches each, the switches of each group being adapted to select out any particular line of a one hundred line group of subscribers to which the switches of the group are assigned. The contact ter- J minals of the connector are, of course, multiplied a large number of times and would ordinarily be multiplied in the present system one hundred times or to each second selector of a one thousand line group. The second selector, operating responsive to currents controlled at the calling substation, selects the group of connectors desired, and then the idle connector, thereby placing it under the control of the calling substation.

The connector, by its wipers, has access .24, forming terminals of a group of one hundred subscribers lines. The contacts of these lines are preferably arranged in ten groups of ten contact sets each, the motion of the Wipers ofswitch D being first in a primary direction in one plane to select a group of contacts, and then in a secondary direction in another plane to select the calling line of the'group. Each group of ten lines, therefore, has a common or group contact 27 controlled by a common relay 18, which contact the wiper 27 engages. The said wiper 27 controls the primary movement of the switch D, the line wipers 21 -21 23 25 moving along with the said wiper 27. When the wiper 27 reaches a group contact 26 belonging to a group of lines among which a calling line is included, the primary movement of all the wipers is arrested and the line wipers 21 -212325 then initiate their secondary movements to select'the individual contacts 2020222 1 of the calling line, wiper 27 remaining quiescent at this time and not partaking of the secondary movement.

As before stated, each group of one hun dred calling lines has associated with it ten line selectors D, so that the contacts 20 20-2224 of each line and the group contact 26 of each group are multiplied ten times, once to each such line selector bank. When the calling subscriber removes his re ceiver, he causes a line selector to start into operation to seek out his line and thereby connect the first selector with said line. This is effected through the agency of the mastersWi-tch C to whose relay 28 each calling line is enabled to transmit current by means of the switch contacts of its line relay 9. The said master-switch, when operated at the initiation of aeall as above indicated, causes an idle selector to start its operation. The line selector then re-acts upon the master.- switch in such manner that its wipers 303 l move away from the switch contacts 31-35 of the line selector which they start, and then keep up an independentprogressive movement over terminals 31-35 of busy line selectors until they reach terminals of an idle one, when the said wipers come to rest. The detailed relation of the difierent parts to one another will be best understood through the narrative of operation.

Assuming that subscriber A is to be connected with subscriber B whose telephone number will be assumed to be 3456; subscriber A first removes his receiver, thereby completing a conductive bridge of limbs P and S by the usual elevation of the hook lever. Relay 9 is energized by current from ground therethrough, normal armature contact 14, over limb P, through hook lever and transmitter at station A, limb S, normal armature contact 16, to battery B. Armature 10 is thereby attracted to engage its switch contact (immediately thereafter. breaking the normal contact of said switch contact whereby substation control of relay 9 is removed) to complete a. locking circuit for said relay, established from ground therethrough, con tact 10, contact 17, relay 18, to battery. Relay 18 'attracts its armature to remove ground from the multiple group contact 26 at each line selector of the ten. Armature 11 disengages its normal contact to remove ground from each of the individual private contacts 20 of the line at the ten line selectors, and the said armature engages its alternate contact, operatively connecting relay 12 with the contact 20. The lower armature of relay 9, engaging its contact completes a circuit from ground through resistance 19, the left-hand winding of master-switch relay 28 to battery, causing said relay to attract its armature and complete an energizing circuit of relay 29, which latter attracts its armature and causes a flow of current as follows: from ground at its armature,

through contacts 3031, contact 40, at an idle line selector D (wiper 30, when resting, always engages contact 31 of an idle line selector as hereafter explained), through relay 37 of said line selector to battery. Relay 37 attracts its upper armature and closes circuit from ground, through resistance 36, right hand winding of relay 28 to battery, whereby the armature of relay 28 is allowed to fall back because the said relay is difi'erentially wound and resistances 36 and 19 are equal. It is apparent that relay 29 is thereon immediately deenergized and its armature retracted. Armature 39 of relay 37 is attracted, closing circuit through vibratory primary magnet PM, which, becoming energized, advances wiper 27 to engage the first group contact 26, wipers 21212325 moving opposite the contacts of the first group, but not engaging any contacts. Relay 37 has attracted its armature 38; and, if the first group contact 26 engaged is in its normal condition (no line in the group then calling), the said contact will be grounded at the armature of group relay 18, and looking circuit is completed for relay 37 from battery, through said relay, attracted armature 38, contact 27-26 to ground via armature of the first (group relay 18. As armature 39 thus continues attracted, magnet PM is, on the retraction of its vibratory armature, again energized and moves wiper 27 to engage the second group contact. If this contact has its normal round at the second group relay 18, relay 3 will continue energized and the preceding process is repeated; wiper 27 engaging the third group contact 26; and so on until the group contact of a calling linethat of subscriber A-is found whose ground has been removed by the previously described operation of relay 18. No locking circuit for relay 37 is then completed, and its armatures are retracted, the armature 39 preventing further operation of primary magnet PM whereby wiper 27 rests engaging group contact 26 of the ten line group including line A, while line wipers 21-2123-25 have moved along with wi er 27 to such a position that they are ad acent to the group of contacts including a line contact set of sub scriber A.

On the first primary movement of the wipers, contacts 40-41-42 of the primary oil-normal switch P. 0. SW. were shifted to their alternate positions, contact 40 opening the original energizing circuit of relay 37. Contact 41 completes a circuit from ground, through contacts 35-34, relay 32 to battery B, causing relay 32 to attract its armature, whereby circuit is completed for magnet 33 of the master-switch, which, by its energization, advances wipers 3034 a step to engage contacts 3135, respectively, of the next line selector, it being understood that the said wipers have in front of them ten contacts 31 and ten contacts 35, belonging in pairs to ten line selectors. If the contact 35 now engaged by wiper 34 belong to a busy line selector-that is, one in which spring 41 has been shiftedrelay 32 will continue energized by current from this second line selector via its shifted spring 41; magnet 33 will step wipers 3034 one step farther, when the above process will be repeated if that line selector is in use; and so on until wiper 34 engages contact 35 of an idle line selector, when its contact 41 will be as shown at D, namely, on open circuit, whereupon relay 32 will become deenergized, preventing further operation of magnet 33, and wipers 30-34 of the master-switch will remain on the contacts of an idle line selector waiting for another call to come'in.

Returning now to primary off-normal switch contact 42, its shifting operatively connects the winding of relay 48 with the normal contact of the upper armature of relay 37, so that on the deinergization of said relay, occurring as before described, circuit is completed from ground at said upper armature, through contact 42, normal contact 45, is thereby energized to initiate the secondary movement of wipers 21--2325 by means of its armature 51 which closes circuit from battery, through secondary magnet SM, armature contact 51, to ground through alternate contact of switch spring 46; springs 4647 of the release switch R. SW. having been previously shifted on the first energization of the primary magnet PM. Wipers 21 21-23-25 engage contacts 202022-24 respectively, belonging to the first line of the group. When it is at normalthat is, when the subscriber is not making a callits multiple contact 20 will be grounded by way of the normal contacts 11-15 of its relays 912; hence, armature 50 of relay 48 being at this time attracted, a locking circuit will be closed from grounded contact 20, wiper 21, attracted armature 50, relay 48 to battery; and armature 51 continuing attracted, secondary magnet SM will, on the retraction of its armature, become again energized, moving wipers 21 --21-2325 to engage contacts 2020-2224 of the second line of the group. If this line is not calling, its contact 20 will be grounded and relay 48 will continue to be locked as before described, a third deenergization and energization of secondary magnet SM resulting, advancing the wipers the third secondary movement, and so until contact 20 of the line of subscriber A is reached, which contact, on ac count of the attracted condition of armature 11 of relay 9, is ungrounded, whereby locking circuit of relay 48 is destroyed, its armature retracted, opening circuit of secondary magnet SM and preventing further movement of wipers 2121-2325 which remain in engagement with the multiple contacts of the calling line; wiper 21 then operatively connecting register magnet a with the contact of armature 77 of E. Armatures 49 and 52 were held attracted during the secondary movement of the wipers in order that wipers 2325, which were then wiping over line contacts of the various lines, might be insulated, so that no disturbance of existing conversations could oc cur. Upon the deenergization ofthe relay 48, they will, of course, be retracted to extend wipers 23-25 to connection with the circuits of the first selector E. Contact 50, upon the deenergization of the relay, by falling back to engage its normal grounded contact, completes a circuit from grounded contact 50, contact 2120 and alternate contact 11, cut-ofi' relay 12 to battery B, energizing the said relay 12 which, by the operation of its armature 13, completes a looking circuit for itself to the same ground at contact 50, while armature 14 completes a circuit from limb P through to Wiper 23. Armature l5 removes the ground from the relay 48 to battery 13. Relay 48 normal contact of armature 11 of relay 9,

thereby preventing a permanent locking of relay 12 which would otherwise occur when a connector engaged contact 6 of the line. Armature 16 in its operation opens the normal connection of battery B to limb S and completes the circuit of said line limb through to wiper 25, while armature 17 opens the prevlously extending series circuit through relays 9 and 18, causing the deenergization of both of them and the retraction of their armaturesthat of relay 18 again grounding group contact 26. Since ground at armature 50 of relay 48 is now connected to the private contact 20 individual to the line, its multiples are now" non-selectable 'by any other line selector.

The secondary off-normal switch S. O.

' SW. contacts 4445 were shifted at the first energization of the secondary magnet SM, spring 45 interrupting the original energ zing circuit for relay 48, while sprmg 44 mterrupts the neutralizing circuit includlng resistance 36, and said spring 45, by engaging its alternate contact, operatlvely associates relay 48 with the normal contact of release switch spring 46 for use in the restoration of the line selector, as hereafter described.

It will be observed that upon the retraction of the armature of relay 37, which in its attracted position originally completed the neutralizing circuit for relay 28, a new path for continuing such neutralization had been completed by the shifting of switch spring 46 occurring on the first actuation of primary magnet PM; the new neutralizing circuit extending from the ground of said switch spring 46, its alternate contact, normal contact of switch spring 44, and resistance 36. This circuit is of course broken on the first energization of secondary magnet SM by the shifting of spring 44, but before that occurred, a third circuit was completed from ground at switch spring 46, its alternate contact, attracted armature 51 of relay 48, and resistance 36. This last circuit continued until the deenergization of relay 48, when the circuit of resistance 36 in the right-hand winding of relay 28 is opened at contact 51; but simultaneously with the opening of this circuit, relay 12 was operated and relay 9 deenergized, the retraction of the lower armature of the latter opening the circuit through the left-hand winding of relay 28. Thus, it will be observed that fromthe time the line selector starts, armature of relay 28 will remain retracted as far as line A and switch D are concerned, first because of the neutralized condition of the relay windings continuing until selection of the line, and thereafter because of the practically simultaneous opening of the neutralizing circuits of its windings.

Thus an untoward attraction of its armature is prevented which, should it occur or exist after wipers 30-34 have reached contacts 3135 of an idle line selector, would cause the initial operation of said selector to no avail, as there would be no calling line for it to make connection with.

The relation of the master-switch to the line selectors and the calling lines which it serves is such that as many line selectors will be started to seek out calling lines as calls come into the exchange, and no more, except in certain rarely occurring instances. It will be observed that if three calls were to come in simultaneously, the resulting energization of the three relays 9 of the lines will cause three resistances 19 to be connectedin circuit with the left-hand winding of relay 28, causing a greater current to flow therethrough than in the case of a single call. The starting of the first line selector, throwing only one resistance 36 into circuit with the right-hand winding, will neutralize one only of these resistances 19; therefore, the armature of relay 28 will continue attracted, and as soon as the wipers 3034 reach contacts 3135 of the next idle line selector, this switch will also be started; there will then be two windings 36 in circuit with the right-hand winding of relay 28, but, there being three windings in circuit with the left-hand winding, its armature will continue attracted; and when wipers 3034 reach the third idle line selector, this one will also be started in search of the third line. As soon as this switch starts, however, a third winding 36 will be included in circuit with the right hand winding of relay 28. The three windings 36 will effectively neutralize the three windings 19, the armature of relay 28 will be retracted, and when wipers 3034 engage contacts of a fourth idle line selector, this switch will not be started.

The amount of time required for the operation of the line selector to connect with the calling line is exceedingly small,requiring (as will be more fully understood when the mechanical features of the switches are described hereinafter) a maximum of thirty step-.by-step movements under the most unfavorable condition, the switches being of such character that this number of steps can be performed in less than a second of time.

Subscriber A, desiring his line to be connected with the line 3456, now operates the calling device to transmit three impulses of current by rotating the said device clock-wise until three of its insulated teeth have passed below spring 3 and then releasing it whereon its associated spring turns the dial in the opposite direction,the three insulated teeth each causing spring 3 to engage and disengage its contact once. With the return of the dial to normal, its insulated tooth at the exmeagre treme left causes spring 2 to engage its associated contact a single time, thereby sending one impulse of-current over limb S, but not until the last tooth at the right has sent the last impulse over limb P. While the dial is at any other than at normal position, the pin shown thereon is brought to such position that tension is removed from spring 4: which then disengages its associated contact, temporarily conductively disuniting the two line limbs P and S at that point in order that impulses may be sent over the line limbs separately. The operation of the dial, as described, sends three impulses of current from ground at the substation, through spring 3 and its contact, over limb P of the line, through attracted armature 14:, contact 2223, armature 49, contact 54 at switch E, upper armature of relay 7 3, contact 55, through the winding of primary relay PR to battery, causing energlzations and denergizations of-s'aid relay whose thrice attracted armature causes three impulses to fiow from ground, through armature spring 57 and its alternate contact, contact 58. primary magnet PM, to battery. The hree resulting energization's of PM move the first selector switch wipers 596061 to positions adjacent to the third group of second selector contacts, terminals of second selectors belonging to the third thousand lines includingthose from 30 00 to 3999. With the first primary movement of the wipers, the primary off-normal switch (P. 0. Sun) contact and the release switch (It. Sw.) contact are shifted to their alternate positions preparatory to the energization of the secondary magnet SM.

With the return of the dial to normal, an impulse flows from ground at the substation, through spring 2 and its contact, over limb S of the line, through attracted armature 16, contact 2425, contact 52, through contact 62 at switch E, lower armature of relay 73. contact 64, winding of secondary relay SR, to battery, causing the attraction and release of said relays armature and a flow of current from ground, through spring 65 and its alternate contact, contact 66 and busy relay BR, to battery. Contacts 6770 are attracted to disconnect wipers 6061 from battery while wiping over contacts of busy second selectors; armature 68 is attracted to close circuit from ground, through the primary off-normal switch P. 0. Saw, the alternate contact of the release switch It. Sw., alternate contact 68, secondary magnet SM, to battery. The secondary magnet, having a vibratory circuit, attracts and releases its armature, the operation bein g effective to move wipers 59-60-61 into engagement with contacts 868788 of the first second selector of the group. With the first secondary movement of the wipers, the secondary off-normal switch (S. 0. SW.)

contacts 58-436 are shifted to operatively disconnect the windings of the primary magnet PM and of the busy relay BR from switch springs 57 and 65 respectively, If the second selector mentioned is idle, it will be in the condition shown in Fig. 1,. Contact 86 being on open circuit, busy re layBR becomes deenergized, armature 68 opens the circuit of magnet SM, and the wipers rest in engagement with the contacts of the first second selector; armatures 67-70 by, their retraction render the said second selector responsive to current to be transmitted by relays PR and SR.

Armature 68, in engaging its normal contact, places direct ground through the primary ofi-normal switch (P. 0. Sun) and release switch (Rm SW.) contacts, normal contact 68, right-hand armature of RM, and wiper 59 upon contact 86 of the second selector and its multiples to render the said second selector busy. It will, therefore, result that should the wipers of another first selector now be brought to engage multiples of contacts 8G-87-88 of the first second selector switch F, busy relay BR of thisother first selector then energized will have its circuit continued in this condition by current flowing from grounded contact 86 to its multiple engaged, the right armature contact of RM, through attracted armature 69 of its busy relay BR, through said relay. to battery. The relay will, therefore, continue to be energized. Secondary magnet SM, by the retraction of its armature, will have its circuit closed and become energized and deenergized a second time, moving the wipers 596061 to engage the contacts of the second second-selector of the group. If this be in use, another locking circuit for busy relay BR will be established as the preceding one is broken; SM

advances the wipers a third step, and so on until contacts of an idle second selector are reached, when, owing to the insulated condition of its contact 86, the denergizing of BR ensues, prevent-ing further operation of SM, and the wipers come to rest.

Returning to the connection being established, subscriber A now operates dial 1 to transmit four impulses of current through relay PR over the above traced path, which said relay is operated four times, transmitting four current impulses from ground, throu h alternate contact 57, normal contact 6 contacts 6087, normal contact 89, normal contact 91, primary magnet PM to battery, causing four energizations of the said primary magnet. The said magnet thereby moves wipers 939495 of the second selector adjacent to a group of contacts, terminals of connectors belonging .to the fourth one hundred group of subscribers lines of the third thousand, this including lines from 3400 to 3499. With the first movement of the wipers, the primary 011'.- normal switch springs 1. O. Sw. are shifted to their alternate positions and also the spring of the release switch R. SW3.

With the return of the dial to normal, a single impulse flows from round at the substation, through relay SR over the before-traced path, said relay being energized and dei nergized to transmit a current im-, pulse from ground, through spring and its alternate contact, through normal contact 70, contact G188, contact 90, busy relay Blt to battery, energizing the said relay. Its upper armature and armature 98 place wipers9+l and 95 on open circuit, While armature 90 completes circuit from ground at the primary ofi'-normal'switch P. O. SW2, through the alternate release switch (R. Sw?) contact, attracted armature 96 and the winding of the secondary magnet SM to battery, causing the energization of said magnet, which is effective to cause Wipers 93-94-95 to engage contacts 99100101 of the first connector of the selected group. If contact 99 belongs to an idle connector, it will be on open circuit as shown at G in Fig. 1. No locking circuit for relay BB will result from the attraction of armature 97, and the armature of said relay falls. back; the upper armature and armature 98 operatively connecting the circuits of the connector with relays PR and SR, rendering the connector controllable from substation A, while armature 96 opens the circuit of secondary magnet SM leaving the wipers in engagement with the terminals of the first connector of the group; and, by the engagement of its alternate contact, said armature 96 places dead ground from the pri mary off-normal switch sprin alternate contact of release switch R. Sw.-,normal contact 96, normal contact of the right armature of release magnet RM contact 9399 upon the multiples of the said contact 99 appearing at the other second selector banks, so that if another second selector F has its wiper 93 brought to engagement with a multiple of contact 99, its relay BB will be locked by current from grounded contact 99 via alternate contact 97 secondary magnet SM then advances the wipers to engage contacts, terminals of the second connector of the group. If this contact 99 belongs to an idle connector, the second selector will stop its secondary movement and the contact 99 will be rendered busy, as described in connection with the second selector F, so that a third second selector seeking a connector in the same group will select the third connector of a group, and so on. Withl the first secondary movement of the Wipers 9394.95, springs 89-90 of the secondary off-normal switch S. O. SW. are shifted to operatively disconnect primary magnet PM and busy relay BB from relays PR and SR. Subscriber A now operates dial 1, transmitting five impulses of current from ground at the substation, through relay PR, causing five actuations thereof which are effective to transmit five impulses of current from ground, through alternate contact 57, contacts 67, 6087, 94 100, normal contact 102, contact 103, through primary magnet PM at the connector G to battery. Five resulting actuations of said magnet are effective to move wipers 105100107 to positions adjacent to a group of ten contact sets in their banks, forming terminals of the fifth group of the one hundred lines which the connector servesnamely, terminals of lines from 3451 to 3459 inclusive, followed by terminals of line 3450, it being understood that zero is represented by ten current impulses. With the first primary movement of the wipers, primary off-normal switch spring I. 0. SW. is shifted to operatively connect contact 99, via normal contact 122, with the winding of the release magnet RM to place the same under control of the calling subscriber, as will-"be hereinafter more fully explained.

\Vith the return of dial 1 to normal, a single impulse is transmitted after the last of the five preceding ones from ground, over limb S, through relay SR, traversing a before-traced path, actuating relay SR a single time, whose armature is effective to transmit a single current impulse as follows: from ground, contacts (35-70-61 889895l01, normal contact 108, lower armature of magnet RM, through secondary magnet SM to battery. The secondary magnet SM is thereby actuated a single time, moving wipers 10510(3107 one step nearer the selected contact group, it being understood that the normal positions of the wipers of a connector are such that after any primary adjustment, they are two steps distant from the first contacts of the group selected.

Vith the first secondary movement of the wipers, springs 102108 of the secondary off-normal switch S. 0. SW. are shifted; 102 to engage its alternate contact, while 108 is shifted only sufiiciently to disengage its normal contact; a second step of the wipers being required to shift it sufiiciently to engage its alternate contact. Subscriber A now operates dial 1 to transmit six current impulses from ground at the substation through primary relay PR, causing six actuations thereof and six current impulses to be transmitted from ground via spring 57, over the before-traced path, contact 102, the impulses then passing via alternate contact 102, normal switch contact of upper armature of relay 109, lower armature of magnet RM secondary magnet SM to battery. The first resulting actuation of secondary magnet SM moves wipers 105-10(3-107,

meagre now on their normal open circuit, to engage contacts 678 of the first line of the group, or line 3451; and with this movement, the complete shifting of secondary off-normal switch spring 108 is accomplished. The succeeding five actuations of SM are etlcctivc only to move wipers 105 106*107 successive steps, the sixth actuation causing them to engage contacts 07-8, multiple terminals of the called line 3450 belonging to subscriber B.

After the transmission of the last of the six impulses, a single impulse is, in the usual manner, caused to flow from ground at the substation over limb S to secondary relay SR, whose actuation transmits an impulse from ground, through contact 65, over the before-traced path to contact 108, thence via its alternate contact and the normal con tact of the lower armature of relay 109, through the left-hand winding of test relay TH to battery, causing the said relay to attract its armature. Let it be first assumed that the called line B is idle, in which case, as shown, contact 6 is connected to battery B through the winding of cut-ofi' relay 12, there being no ground connection to the said contact except through battery. The attraction of the right-hand armature of test relay TR connected its right-hand winding from battery, through said attracted armature, normal contact 10%, normal contact 110, wiper 105 to contact 6; but since this contact is already connected to battery, upon the cessation of the impulse transmitted by secondary relay SR, test relay TB is decnergized, its armatures falling back, this being efiective to shift springs 110-111 of the test switch T. SW. The shifting of spring 110 connects ground to wiper 105, contact 6 and its multiples, completing circuit through cut-oft relay 12 of called line B, to battery. The resulting attraction of armatures 14:16 complete the circuit over limbs l and S of the called-for line to contacts '2"8. That of 14 also disconnects line relay 5; from limb P of the line, so that when the called subscriber l3 removes his receiver, 1 he act is ineii'cctive to operate relay 0 which would otherwise cause a line selector to selcct his line. The placing of ground, just described, upon contact 0 and its multiples from spring 110 renders the called line busy with respect to other connectors as will be hereafter more fully explained; ground from contact 6 being also connected via armature 13 to contacts 20 of the called line, keeping themunselectable in character.

The shifting of test switch (T. SW.) spring 111 completes circuit through relay 109 from ground, spring 111, contact 115, ringing relay 112, to battery B On the resulting attraction of the armatures of relay 109, a circuit is completed from ground through normal contact of the lower armature of relay 11?, normal contact 119, attracted armature of relay 109, alternate contact 102, contacts 1009d, 8760, contact 67, normal contact 5?, contact 71, magnet 73 to battery, causing the encrgization of said magnet 73 whose attracted armatures complete a bridge of battery B in the line of subscriber A from ground through upper windings of relays l t- 75, attracted upper armature of relay 7 3, contact 54:, to the left over the heavily marked conductor, contact 62, attracted lower armature of relay 73, lower windings of relays 7 5-74 to battery. Differentially connected relay 7 1 is not energized, the flow in its two windings being equal, but cumulatively connected relay attracts its armatures, of which 56 and 63 complete parallel paths from ground and battery to limbs P and S respectively, while contacts 55 and 6t disconnect relays PR and SR from the talking circuit.

Having explained the effect of the shifting of spring 111. at G with respect to the first selector, ll will now describe its effect with respect to the called line. Its shifting energizes ringing relay 112 over a beforetraced circuit, and the attracted armatures of said relay cause alternating current to flow from generator G2, upper armature of relay 112, contact 1067, relay Z) and noninductive resistance 0 in parallel, alternate contact 14:, limb P of the line of B, normal hook-switch contact, bell and condenser, limb S, alternate contact 16, contact 8-107, attracted lower armature of relay 112, lower winding of relay 113 through battery B The interrupter I is provided in the circuit of generator G so arranged as to periodically connect the said generator in and out of circuit with said line in the wellknown manner It will be observed, however, that the brushes of T are so arranged that at all times during the ringing, ground is connected to limb P of the rung line either through generator or the grounded brush of the interrupter.

It should be observed that the characters of relays 113 and Z) are such that the flow of generator current through the substation condenser does not actuate the relays. As soon, however, as the called subscriber answers the call by removing his receiver, the substation hook lever engages its alternate contact, completing a conductively continuous circuit from ground through gcnerator G or interrupter 1 as the case may be, to limb 1 over the before-traced path for ringing current, the alternate contact of the hook lever and through the transmitter, returning over the limb S and thence over the before-traced path and the lower Winding of relay 113 to battery 13*. Current flowing over this conductive circuit energizes relay 6 and relay 113, whose attracted armature 1141 first completes, by engaging spring 115, a

locking circuit including serially the already energized relay 109 and the upper winding of relay 113, causing both relays to remain energized, the said armature immediately thereafter breaking the normal contact 115, thereby effecting the deenergization of ringing relay 112 and the immediate exclusion of generator G from connection with the called line. The attraction of the lower armature and armature 116 of relay 113 bridges relay 117 across the called-for line, which relay is immediately energized by current flowing over said line. The lower armature of relay 117 disengages its normal contact whereby the before-traced circuit through magnet 73 at E is interrupted and the said magnet is dei nergized, the consequent retraction of its armature shifting springs 5171 and 6272 to their alternate positions. The deenergization of relay 73 does not effect the continued energization of relay 7 5 on account of the parallel path of current, before indicated, through said relay. Springs 541 and 62, in disengaging their normal contacts, prevent relays PR and SR from again being connected to the calling line by the retraction of the armatures of 73; and in engaging their alternate contacts, said springs 5462 complete the talking circuit of switch E. Spring72, in engaging its alternate contact, completes a path for energizing relay 76, which relay, by the attraction of its armatures 76 and 79 to engage their associated 7 contact springs, thereafter breaking the normal contacts of said springs, reverses the connections of battery B to the calling line, causing a reverse flow of current thereover through the substation. The attraction of armature 7 7 completes circuit through register magnet a, causing it to attract its armature to bring pawl a. into engagement with the next tooth of its associated ratchet, in order that on the .deenergization of magnet a and the retraction of its armature, pawl a may advance the ratchet a step, causing a completed call to be recorded against the line of A as a calling line upon the associated counter a Returning now to relay 117 at G, having explained the effect of the lower armature of said relay in disengaging its normal contact, it will be observed that the said armature, engaging its alternate contact, completes a circuit from ground through relay 118; said relay 118, by the attraction of armature 121, establishing a locking circuit for itself through switch spring 110 of the test switch T. Sw., to ground. Armature 119 completes the talking circuit to wiper 106; armature 120 closes a break in the circuit of release magnet RM while armature 122, in leaving its normal contact, removes the previously existing control of release magnet RM from the calling substation, and by engaging its alternate contact, places an in- B are now in conversation, circuit being traced from substation A to substation B by means of the heavily marked conductors and condensers 8182 through the exchange, talking battery being supplied to the calling line through the impedances of relays 7 47 5, and to the called line through the im-,

pedances of relay 117 at the connector.

When the subscribers have finished their conversation, they replace their receivers upon the hook levers; the act of subscriber B in so doing restores theconnector G to normal, while the act of subscriber A in so doing restores line selector D, first selector E and second selector F to normal. When subscriber B replaces his receiver, the operation of arm 5 of the hook lever upon its associated contact springs momentarily grounds limbs P and S in the usual manner, but this operation is not used to cause the release at the called substation. The replacing of the receiver causes the hook lever to disengage its alternate contact, opening circuit through relay 117, held energized by current over the line during conversation. The upper armature of relay 117 then falls back and completes a circuit through release magnet RM from ground, through contact 120 of relay 118, upper armature contact of relay 117 to battery, effecting the energization of the release magnet whose armature is thus attracted, shifts the switch springs 110-111 to normal, opening the circuit of relays 109-113118, causing their deenergizations. The deenergization of relay 118 opened the circuit of release magnet RM whose armature thereupon is retracted and wipers 105106-107 allowed to return to normal, their restoration causing on its completion the shifting to normal of the primary off-normal switch P. O. Swf, the secondary oil-normal switch springs S. 0. SW. being restored at the time the wipers have been restored as to their secondary movements. As soon as the conductive circuit is opened at substation B, magnet I) is denergized; and the armature of said magnet, previously attracted on the energization of the magnet to cause pawl b to engage the next tooth of its adjacent ratchet, is now retracted, causing said pawl b to advance its ratchet a step and thereby count one completed call upon register 12 against line B as a called line.

lVhen the calling subscriber replaces his receiver, arm 5 temporarily grounds limbs P and S of the line,- the grounding of limb S short circuiting the upper winding of difierential release relay 74; and current continuing through the lower winding of said relay to ground at the substation, its armature is attracted to complete circuit through release magnet RMat switch D; from ground, attracted armature of relay 74, release magnet RM of switch E to battery. The energization of magnet RM shifts springs 5471 and 62-72 to normal, the shifting of spring 72 deenergizing magnet 70, whose retracted armature 77 opens circuit through magnet a, so that its retracted armature effects a thrust of awl a to turn its ratchet a step and recor a call on counter a". The attractedright-hand armature of release magnet RM closes circuit through release magnet RM at second selector 1*, from ground through the shifted primary off-normal switch (P. 0. SW?) contact, contact 86-59, attracted armature of RM to battery. The release magnets of all the switches D, E and F are now energized and their energizations shift to normal the various release switches R. Sw., R. Sw., and R. SW3; the shifting of said switches causing, respectively, the energizations of relays 48, BR and BR whereby the wipers of the various switches are disconnected from battery and so held during the release of the switches. In the restoration of the hook lever at substation A, arm 5 in passing from the top of its associated contact spring removes ground from the two limbs of the line and the armature of relay 74 returns to normal, deenergizing release magnets RM and RM, the deenergization of RM opening the circuit of RM. The deenergizations of the various release magnets RM, RM" and RM cause the restoration of the wipers of the various switches with which they are associated. When the switches have reached normal as to their secondary movements, the secondary off-normal switches S. O. Sw., S. 0. SW. and S. O. SW. are restored; when the wipers have been restored as to their primary movements, the primary off-normal switches P. 0. SW., P. 0. SW. and P. O. Sw. are restored. The restoration of the primary off-normal switches respectively cause the deenergizations of relays 48, BR and BB reestablishing the normal connections of the wipers. It should be noted that the armatures of RM, when attracted, keep the line limbs PS connected to the windings of relay 74, while the energization of relay 48 by armature 50holds relay 12 energized.

Assuming now that, at the time Wipers 105-100107 came to rest engaging contacts 678 of the called line, this line was a busy line. In such case, ground will be connected to contact 6 and its multiples via the shifted test switch (T. Sw.) contact'110 of another connector (if the busy line be a called line), or via armature 13 pertaining to the busy line, its contact 20, wiper '21 of a line selector then connected thereto,

to ground through contact 50 at the said line selector (if the busy line be a calling line). In either case, upon the energization of the test relay TR at switch G, as before described, the said relay, instead of being thereon deenergized, will have its armatures locked in their attracted positions by current from grounded contact 6, wiper 105, normal contact 110, contact 104, right armature of relay TR, its right winding to battery. The test switch contacts therefore remain at normal and a busy signal is transmitted to the calling subscriber from interrupter I through the induction coil and condenser, left armature of relay TR, normal contact of lower armature of relay 109, to the left over the talking circuit indicated by heavy lines, to switch E, via normal contact 70, condenser 83, to the left over the heavil marked talking conductor, limb S of the line of A, through the transmitter and the primary of the induction coil, causing an audible signal in the receiver, returning over limb P, to the right over the upper talking conductor, normal contact 54, normal contact of relay 73, armature 55, relay PR through battery B. The calling subscriber, in response to this signal, replaces his receiver, momentarily grounding the two limbs of his line. Inasmuch as relay 7 3 has not been energized, relays RR and SR are still operatively connected to line limbs P and S respectively and they are therefore, on the grounding of the line limbs, both simultaneously energized to close contact 8485.' Circuit is then completed from ground at release magnet RM of the line selector, contact 8584, release magnet RM of the first selector to battery. RM attracts its armature, closing circuit from ground at release magnet RM of second selector F, through alternate contact of primary off-normal switch P. O. SWF, contact 8659, attracted armature of RM to battery. The attracted armature of RM closes circuit from ground through RM at the connector, normal contact 122, the shifted contact of primary off-normal switch P. O. Swfi, contact 99-93, attracted armature of RM to battery. The armatures of all the release magnets are now attracted; and when ground is removed from the two line limbs at substation A, the resulting deensubscriber for removing the calling subscribers control of RM -consists of armature spring 122 of relay 118, which, when actuated, by disengaging its normal contact, opens a contact in the circuit of RM and thereafter puts the second busy potential upon'contact 99, as before described.

From the release operations already described, it is apparent that as soon as the line selector has selected his line, the calling subscriber may, by grounding the two line limbs simultaneously, cause the closure of contact 858l, which will be effective to release whatever switches are connected to his line, so that, whatever stage of completing a connection may have been reached, the release of all switchesso far operated may be secured.

It may sometimes happen that a line selector will overrun on its primary or secondary movement through accident or certain rarely occurring combinations of circumstances. To take care of, these occurrences, I have provided the two switch springs 43 and 53; the former being so related to the switch mechanism that, if the switch shall make an eleventh primary movement, the contact 43 will be closed; while if the switch makes an eleventh step in its secondary movement, the contact of 53 will be closed. In either case, a circuit will be completedfrom ground through the release magnet RM, contact 43 or 53, as the case may be, alternate contact 47 of the release switch R. Sw. to battery, energizing release magnet RM, upon whose energization the release switch R. Sw. will be shifted to normal, spring 47 then opening the circuit- {employed only to successively cross the individual contacts 31 and 35 to the respective common contacts 30 and 34, leading (as shown in Fig. 1) to the armatures of relays 29 and to relay 32. The said wipers 30 and 34 are fastened to a rotatable ratchet 30 adapted to be driven, step by step, by the armature-actuated pawl 30 of magnet 33, the magnet being provided with an interrupter actuated by its armature, as shown.

A line selector (Figs. 4, 7, 8 to 11 inclusive) comprises essentially ten group contacts 26 and a group wiper 27 making primary movements only, a contact bank including one hundred sets of contacts 20 22-2024, arranged in ten groups of ten sets of contacts each, a set of wipers 21- 232521, capable of primary movements to select a group and secondary movements in an intersecting plane to select a contact set of a group, a primary off-normal switch P. 0. SW. comprising switch springs shifted on the first primary movement of the wipers, a secondary ofi-normal switch S. 0. SW. comprising switch springs shifted on the first secondary movement of the wipers, a release switch R. Sw. comprising springs shifted on the first primary movement of the wipers, a primary over-run switch shifted when an eleventh primary movement takes place and a secondary over-run switch shifted when an eleventh secondary movement takes place.

A sectional view of a bank seen from the left is given in Fig. 9 and a front view in Fig. 10, a contact set 20222024 (Fig. 9) being indicated by a single short line in Fig. 10. The one hundred sets of contacts, as indicated in Fig. 10, are arranged as if projecting through the inner surface of a section of a hollow sphere.

In their primary movements, the wipers 2123-25 21 are rotated step-by-step from left to ri ht, each step bringing them opposite a difierent group. or upright section of ten contactsets; and in their secondary movements, the wipers are rotated stepby-step upward over the contact sets of the selected row, successively engaging them.

The wipers are pivoted at 23 to a hearing 23, clamped to a rotatable primary shaft PS suitably journaled to the main frame; while a rearwardly extending portion of the wipers, provided with a roller, engages a broad piece 160 fastened to the secondary shaft SS, the secondary movements of the wiper ends being effected by the downward movement of shaft SS, piece 160 rotating the wipers about the pivot at 23".

A suitable spring 161 is fastened to the primary shaft PS against whose tension it is turned, while spring 23 is fastened to the wipers against Whose tension the secondary movements are performed. These springs serve, when the switch (by the withdrawal of the retaining detents hereafter described) is released, to restore the primary and secondary shafts and consequently the wipers.

The auxiliary or group selecting wiper 27 is fastened to the primary shaft, bein solely controlled thereby, and has its row of group contacts 26.

The primary off-normal switch P. 0. SW. comprises an arm fastened to the primary shaft and provided with a stud of insulating material, as best shown in the top view (Fig. 8), holding springs 42414O in their normal positions, shaft PS under the influence of spring 161 pressing the stud against spring 42. The first step of the shaft, which is clockwise, moves the stud away from spring 42 and the three springs 4241-40, by their owntension, are shifted to their alternate position.

The operation of the primary over-run switch will be understood from an inspection of Fig. 7, wherein shaft PS is at normal. The movement of the shaft in the operation of the switch is clockwise, and stud 43 on the eleventh clockwise step of shaft 7 PS comes against and presses the spring 43 of the primary over-run switch to engage its alternate contact.

The secondary off-normal switch is best shown at S. 0. SW. in Fig. 10, comprising an arm clamped to secondary shaft SS extending to the right to hold, in its normal raised position, a stud of insulating material extending through the switch frame and engaging the secondary off-normal switch springs 44 and 45. With the first step of secondary shaft SS, downward in direction, the arm of the secondary off-normal switch is brought downwardly so that springs 44 and 45 press the stud down and engage their alternate contacts.

The secondary over-run switch comprises the stud 53 fastened to secondary shaft SS and so placed that on the eleventh secondary movement it engages spring 53 and presses it into engagement with its associated contact.

For rotating the primary shaft PS, a circular ratchet 124 (Fig. 4) is provided, adapted to be turned step by step by the armature-driven pawl 123 of primary magnet PM, whose vibratory circuit-breaker is indicated at 126.

As well shown in Fig. 9, the secondary shaft SS has cut on its inner surface a ratchet adapted to be engaged by the armature-driven pawl 127 of secondary magnet SM, by successive thrusts of which the shaft may be moved downwardly. The secondary magnet has, like the primary magnet, its armature-actuated circuit-breaker.

A pivoted retaining detent is provided for each shaft, that of the primary shaft being indicated at 125 of Fig. 4, and that of the secondary shaft at 128 (Figs. 4 and 11). These detents have rearwardly extending portions normally engaged by orifices in release arm 130 (Figs. 4 and 11) and are by said arm normally held away from their respective ratchets. On the first actuation of primary magnet PM, its armature effects movement of the pivoted member 132 (see Fig. 4) whose roller end (see Fig. 11) tilts pivoted arm 131 to lift arm 130 to disengage detents 125 and 128 when their associated springs move them to engage their ratchets. They then serve to hold their respective MEL shafts against back movement, keeping them in whatever position they may be placed by the primary or secondary magnets.

The release switch springs 46 and 47 11) are held in their normal ositions by a hook at one end of arm 131. he first actuatlon of primary magnet PM, by operating arm 132, tilts the right end of arm 131 down, sprlng 46 is released and the two springs 46 and 47 by their tension move to engage their alternate contacts.

The release magnet RM has (as best shown in Fig. 11) a pivoted'arm 130 whose left end an associated spring tends to depress. On attraction of the armature of (Fig.

RM, arm 130 is drawn to the left, two orifices therein (shown in the top view, Fig. 4) slipping over the rearwardly extending portions of detents 125 and 128. At the same time, the button of insulating material on the right end of arm 130 restores springs 46 and 47 by engaging spring 46 to move it to be caught and held by the hook of arm 131. When magnet RM is now deenergized, its retracted armature draws arm 130 to the right, which, keeping its hold on detents 125 and 128, moves them away from their shaft ratchets so that the shafts are now free to be restored, shaft SS by spring 23 fastened to the wipers, and shaft PS by spring 161.

A spline 170 (Figs. 4 and 9) is provided on the secondary shaft engaging, with the first movement thereof, any adjacent tooth of ratchet 124 to hold the primary shaft against return movement, to the end that on the restoration of the shafts as described, the secondary shaft may be first completely restored clearing the wipers from the bank, whereon spline 170 releases the primary shaft and permits its restoration.

The primary and secondary off-normal switches are of course restored by the respective shafts when they reach normal, the rf'iestoration of the secondary one occurring rst.

Recapitulating the principal operations; the first actuation of primary magnet PM rotates the wipers a step, shifts the primary off-normal switch, releases the primary and secondary shaft detents and shifts the release switch. Subsequent actuations of said magnet serve only to advance the wipers successive primary steps until a possible eleventh step, when the over run switch is shifted. The first actuation of secondary magnet SM advances the line wipers a secondary step, shifts the secondary ofi-normal switch, and interlocks spline 170 with ratchet 124. Additional actuations of said magnet merely advance the line wipers additional secondary steps until a possible eleventh step when the secondary over-run switch will be shifted. The release magnet when energized shifts the release switch togeneral, similar to that of the line selector The vibratory interrupter of the primary magnet and the group selecting wiper and contacts are omitted. a

The primary off-normal,v secondary offnormal and release switches are controlled in a manner similar to those of the line selector, and the adjustment of the line wipers is mechanically similar. The spring combinations of thevarious off-normal and release switches correspond, of course, to those indicatedat E in Fig. 1.

In Figs. 5 and 6 is shown the mechanism associated with the first selector for shifting springs 7154 and 7262, described in connection with Fig. 1. Said springs are mounted as indicated in Fig. 5, the view showing the springs at'normal. The two insulated studs 135 are drawn to the left to shift the springs, and when they are freed the tension of the springs restores the studs and springs. The studs 135 are fastened to an arm 134: (Fig. 6) pivoted as shown, and having a small projection on its lower extremity adapted to be engaged by the hook of arm 133 when the armature of magnet 73 is attracted. When said magnet is thereafter denergized on the response of the called subscriber, its 'retracted armature causes arm 133 to draw the lower portion of member 134 to the right, whereby studs 135 move to the left to shift their springs.

The operation of release magnet RM is similar to that of magnet RM. of the line selector, except that its armature carries an arm 136 adapted, when the armature is attracted, to engage and lift hooked arm 133 free of member 13 1, thus allowing the restoration of studs 135.

It will be remembered that the shifting of spring 72 (see Fig. 1) energizes relay 76, whose energization causes that of the magnet a. The latter should preferably not be operated when a calling subscriber has connected hisline with an idle called line and fails to secure an answer, as it is desired that answered calls only be recorded. Under such circumstances, magnet 73 is energized as soon as connection is made with the called line, and its deenergization follows when the calling subscriber replaces his receiver, causing the energization of release magnet RM, which, by shifting spring R. SW. energizes relay BR whose armature opens the circuit of magnet 73. The previous energization of 73 has caused arm 133 to engage member 1341 (see Fig. 6). The energization of magnet RM, preceding the deenergization of magnet 73, is effective to cause arm 136 to lift arm 133 free so that the denergization of magnet 73 (occurring while magnet RM remains energized) is ineffective to move memher 134; spring 72 and the other associated springs remaining at normal, whereby an improper operation of magnet a is avoided.

The second selector is mechanically similar to the first selector, except that magnet 73 is not employed, the various off-normal and release spring combinations being arranged as indicated'at F in Fig. 1.

The connector shown in Figs. 12-13-11 relay TR, has a raised portion adapted,

when the armature is attracted, to clear spring 111, the spring associated with arm 137 then causing the upraise to engage said spring 111. On the denergization of relay TR, the springs 111 and 110 are of course shifted by arm 137 for the purposes herein before indicated. When release magnet RM attracts its armature, piece 138 fastened thereto draws arm 137 down so that its upraise frees spring 111 and the two springs 110-111 by their tension return to normal. Moreover it will be observed that when test relay TB is locked because the switch wipers have engaged terminals of a busy line, the energization of the release magnet RM (occurring when the calling subscriber replaces his receiver) will be effective by piece 138 to withdraw arm 137 from engagement with spring 111 so that the springs remain unshifted.

From the foregoing, it is seen that the counter a of a line is operated to register only when the line (as a calling line) has completed a call and secured an answer; and that if the calledline be busy or, being idle, an answer is not secured, means are provided whereby the operation of counter a is prevented. Also counter b is operated to register a call only when a response is made from the called substation. If the called line be busy and another subscriber 

